Personal protection from exposure to harmful chemical and biological agents is often of concern to firefighters and similarly situated personnel. Such protection often includes the use of apparel that provides a barrier to such agents. Butyl rubber is often used in standard protective clothing. However, garments made from butyl rubber are bulky and nearly impermeable to air and moisture (I. Lee, Yang and Wilusz; Polymer Engineering & Science, 1996, 36, 1217), resulting in unbearable levels of heat inside the garments during use.
Various permeable materials having a wide range of mechanical and transport properties are known. Depending upon the particular application in which the permeable material is to be employed, however, certain combinations of properties are required. For example, in a protective apparel application, it is desirable that the material may transport water vapor and block the transport of harmful chemicals and/or biological agents, and be lightweight and flexible over a broad temperature range. A need exists for a material that can be a flexible, solid material with membrane characteristics that facilitate the transport of water vapor, for example, from a wearer of membrane-containing apparel to the atmosphere; allow moisture to permeate the garments to the extent necessary to afford comfort to the wearer, thus reducing heat stress; and block entry of certain chemical compounds and biological agents.
Various references describe semipermeable materials produced from a variety of polymers that may be useful for protective garments. See, e.g., U.S. Pat. No. 6,579,948.
Many previous permeable membranes are microporous (i.e., permeable due to the presence of microscopic pores through which vapor can pass). Microporous membranes, which may be laminated on or between nonwoven textiles, have increased comfort, but may not provide adequate barriers because of their nonselective permeability. They may also have low tear strength and their surfaces may be easily fouled.
Because no single material has emerged which satisfies all of the technical requirements and that presents a cost-effective alternative, it is desirable to provide a selectively permeable membrane or structure or layer that displays a combination of mechanical properties, low temperature flexibility, selective transport, ease of processability, and cost-effectiveness, so as to render it suitable for use in a wide variety of applications.